Corrosion Resistance and Pitting Behaviour of Low-Carbon High-Mn Steels in Chloride Solution

Abstract

CorrosIon rEsIstanCE and pIttIng bEhavIour of low-Carbon hIgh-Mn stEEls In ChlorIdE solutIonCorrosion resistance of the X4MnSiAlNbTi27-4-2 and X6MnSiAlNbTi26-3-3 type austenitic steels, after hot deformation as well as after cold rolling, were evaluated in 3.5% NaCl solution using potentiodynamic polarization tests. A type of nonmetallic inclusions and their pitting corrosion behaviour were investigated. Additionally, the effect of cold deformation on the corrosion resistance of high-Mn steels was studied. The SEM micrographs revealed that corrosion damage formed in both investigated steels is characterized by various shapes and an irregular distribution at the metallic matrix, independently on the steel state (thermomechanically treated or cold worked). Corrosion pits are generated both in grain interiors, grain boundaries and along the deformation bands. Moreover, corrosion damage is stronger in cold deformed steels in comparison to the thermomechanically treated specimens. EDS analysis revealed that corrosion pits preferentially nucleated on MnS and AlN inclusions or complex oxysulphides. The morphology of corrosion damage in 3.5% NaCl supports the data registered in potentiodynamic tests.

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“…The twins represent regions characterized by different potential from the matrix and this leads to the increase in the corrosion current density. Results of our previous works [9,10] confirmed that corrosion pits nucleated mainly at grain boundaries and deformation bands in cold deformed steels. Corrosion resistance of grain boundaries is poor because of high dislocation density present at these regions [17,33].…”

“…Thus, better corrosion resistance of this steel can be also probably related to higher amount of AlN inclusions (and smaller quantity of MnS inclusions). Based on our previous results of potentiodynamic tests [9,10] it can be observed that corrosion pits did not form on Al 2 O 3 inclusions during corrosion tests in 0.1M NaOH in opposite to 3.5% NaCl solution. Park et .…”

“…Chemical composition of steel, especially metallurgical cleanliness related to the amount of non-metallic inclusions, has a significant effect on its corrosion resistance. Previous studies [10][11][12][13] demonstrated that non-metallic inclusions, mostly sulfide inclusions, affect the corrosion resistance of steel by providing pitting sites. That way, special focus should be paid to controlling the amount of sulfur content during metallurgical processes.…”

“…Manganese occurs also with silicon and aluminium additions characterized by high affinity to oxygen (aluminium also to nitrogen). Results of our previous works [9,10] showed that corrosion pits were formed at complex inclusions such as MnS+AlN, oxysulphides containing Mn, Al, N, Si and oxides containing Mn, Al, Si.…”

“…Silicon addition has a negative effect on the corrosion resistance of steels [7,8]. Our previous studies [9,10] demonstrated that a presence of sulfide compounds, especially MnS inclusions, affects the corrosion resistance of steel by providing pitting sites. The same effect was observed in stainless steels by other authors [11][12][13].…”